Dead chick with squishy neck lumps

Hello everyone, I'm new to this forum and relatively new to raising chickens and I hope you can help!!!

I found one of my 2-week old white rocks dead this morning. They all seem normal and healthy but the dead one seems to have an rather large lump on the front of its neck. The squishy lump is about the size of a small apricot or a cotton ball and is just under the skin.

I haven't cut into it yet to see what's going on inside.

Now that I look closely at the others I can see that a number of them have a squishy, liquidy mass on their necks. The lumps all seem to be slightly off to the right side of the neck. The lumps on the live chicks are normal color and have feathers but the lump on the dead chick was pink.

I just opened it up and the crop was just full of normal feed (good organic chick starter). The only other thing it could eat is its bedding (wood shavings), but they don't seem to be interested in those.